Converting bituminous binders in cationic or anionic emulsions is a well-known technique. The emulsion consists of a dispersion of fine bitumen globules in a continuous aqueous phase. The emulsion is called anionic or cationic according to the total electrical charge surrounding the globule which can be negative or positive. In the presence of a continuous electric current, the micellae of bitumen of an emulsion settle on the anode if the emulsion is anionic or on the cathode if the emulsion is cationic.
The conversion of bituminous binders to emulsion makes use of emulsifying agents that favor the dispersion of the globules of binder in the aqueous phase by forming a charged protective shell that prevents their agglomeration.
In the case of anionic emulsions, the emulsifying agent is of the anionic type and preferably consists of a fatty acid alkaline salt. This emulsifying agent is generally mixed with the bituminous binder in a quantity of from 0.05 to 2% by weight. The binder containing the emulsifying agent is then dispersed in an alkaline aqueous phase by passing into an emulsifier.
Cationic emulsions are obtained by using cationic emulsifying agents, which generally consist of nitrogenized organic compounds such as fatty amines, fatty amidoamines, fatty imidoazolines, fatty mono and diquaternary ammonium compounds and reaction products of one or more of said products with ethylene or propylene oxide. The fatty radical of the emulsifying compounds can possess a very diversified chemical structure and the raw materials for the preparation of the emulsifying compounds can originate from different sources such as animal fats, refined petroleum products, vegetable oils and liquid resins. The cationic emulsifying agent is generally dispersed in water to which hydrochloric acid is added. The hydrochloride formed is soluble. The homogeneous solution thus obtained, having a pH generally comprised between 1 and 5, is then put into contact with the bituminous binder in an emulsifier in order to form the emulsion.
Regardless of whether it is anionic or cationic, the emulsion is considered to be a means that allows lowering the viscosity of bituminous binders. The emulsion restores, after rupture, the bituminous binder to which has been added the emulsifying agent used for producing the emulsion. The presence of this emulsifying agent in the bituminous binder is regarded as exerting a favorable effect on the adhesiveness of the binder in the presence of mineral surface, provided it is within a narrow range of pH comprised between 1 and 6.
The largest sale of bituminous emulsions is mainly in the area of building and repair of roads, and essentially in the form of cationic emulsions. Experience in this field shows that cationic emulsions are easier to apply and prevent the numerous inconveniences of anionic emulsions such as the possibility of restoration to emulsion in the presence of water, of unforeseeable rupture in storage and of weak adhesiveness of the binder to the surface of the aggregate.
Cationic bituminous emulsions are mainly used according to two type of technique, namely, coating and encasing.
Coating consists in gluing layers of fine gravel on the surface of the road by means of the bituminous emulsion in order to produce roughness and make the surface impervious. This technique contributes to the creation of a new runway layer.
In encasement, the bituminous emulsion allows the use of layers having a thickness of from 0.4 cm to more than 20 cm, which integrate in all levels of a road structure.
At present, due to the general reduction of budgets for repair and building of roads, the use of the bitumen emulsion is particularly limited to the repair of the surface of roads. However, due to the extreme mechanical demands to which are subjected the mosaics of the surface coatings, the road bitumens of emulsifiable kinds do not have the characteristics necessary that will allow them to bear the tangential stresses due to heavy loads and heavy traffic.
Under these circumstances, the bituminous binders exclusively constituted of bitumen are being increasingly replaced by bituminous binders of the bitumen/polymer type. The bitumen/polymer binders are products obtained from bitumens to which polymers have been added and have eventually been modified by the latter. Optionally, a reagent such as sulfur or a modifying agent and/or an adjuvant can also be present.
Examples of bituminous binders of the bitumen/polymer type comprise preferably:
bitumens modified by olefinic polymers or by mixtures of fatty acids and higher alcohols (French Patent No. 7,627,936 publication No. 2,364,960] of Sept. 17, 1976);
bitumens modified as above and on which have been grafted elastomers (French Patent No. 7,627,937 [publication No. 2,364,961] of Sept. 17, 1976);
bitumens modified by norbornene (French Patent No. 7,630,316 [publication No. 2,367,102] of Oct. 8, 1976);
bitumens modified by dihalopolybutadienes serving as receptive structures to block copolymers and to covulcanizable elastomers (French Patent No. 7,806,160 [publication No. 2,418,812] of Mar. 3, 1978);
bitumens modified by block copolymers styrene/butadiene or styrene/isoprene (French Patent No. 7,639,233 [publication No. 2,376,188] of Dec. 28, 1976);
bitumens modified by block copolymers styrene/carboxylated diene (addition No. 7,831,689 [publication No. 2,440,967] of Nov. 9, 1978 to French Patent No. 7,639,233);
bitumens modified by polyethylene waxes (French Patent No.
[publication No. 2,405,288] of Oct. 5, 1977);
bi-tumens modified by elastomeric acrylic polymers (French Patent No. 7,812,135 [publication No. 2,424,301] of Apr. 25, 1978;
bitumens modified by polymers of the type polyvinyl alcohol, polyamide, polyester, polyurethane;
bitumens modified by olefinic copolymers, preferably among them, ethylene/propylene copolymers or ethylene/propylene/diene copolymers, or by copolymers of olefins and of vinyl monomers, preferably ethylene/vinyl acetate copolymers, ethylene/acrylic ester copolymers, ethylene/vinyl chloride copolymers;
bitumens modified by special polymers of the type of halogenated polymers and preferably fluorinated polymers such as poly-tetrafluoroethylenes or fluorinated and chlorinated polymers, or of the type of silicon polymers such as polysiloxanes;
bituminous compositions obtained by bringing into contact one bitumen with a mother solution containing one polymer, preferably one block copolymer styrene/conjugated diene and sulfur or a polysulfide or another reactive agent, preferably vinyl monomer, as well as a petroleum fraction and/or a coal oil (French Patents No. 7,818,534 [publication No. 2,429,241] of June 21, 1978 and No. 8,210,095 [publication No. 2,528,439] of June 10, 1982; French Patents No. 7,910,987 [publication No. 2,455,623] of May 2, 1979 and No. 8,216,433 [publication No. 2,533,935] of Sept. 30, 1982);
bitumens modified by a mixture of at least two of the polymers cited above, and mixtures of said modified bitumens.
However, the emulsification of said different bitumens modified by the incorporation of polymers cannot be effected as such, since the improvement on the properties of the bitumens systematically increases the viscosity of the medium, which hinders the preparation of binders modified by polymers making use of the conventional industrial equipments. Under these circumstances, it is necessary to use one or several fluidizing solvents, the main part they play being to reduce the viscosity of the medium and bring it to a range equivalent to that of operation of bitumens of penetration 80/100 and 180/220 between 100.degree. C. and 150.degree. C., that is, 1 to 10 poises. The solvent or solvents selected have among other properties that of being partially volatile while preserving the heavy fractions of plastifying and compatibilizing properties between the polymer and the bitumen.
The applicant has observed that the formulation of emulsions of quick rupture from binders of the bitumen/polymer type fluidized or fluxed by oils of petroleum origin or resulting from the distillation of coal in the presence of conventional cationic emulsifying agents such as those mentioned above, led to emulsions in which the rupture is poor or uncertain. It has been observed, on the other hand, that this rupture was represented by a partial coagulation of the bitumen globules without ever resulting in the first hours, even after several days, in the total coalescence of the micellae of the emulsion, and this, whatever the type of emulsifying agent used and the concentration of said emulsifying agent. This deficiency confers on the residual bituminous binder mechanical characteristics which are very inferior to those of the original anhydrous bitumen/polymer binder. Therefore, it limits the development of the emulsions of bitumen./polymer binder in the field of producing thin and superficial coatings on roads having very heavy traffic. The applicant has demonstrated in addition that the phenomenon exclusively depended on a double interaction between the solvent and the emulsifying agent for a conventional emulsifying agent such as defined above and between the solvent and the salts contained in the water, namely, alkaline earth salts and metallic salts. The nature of the bitumen and its origin, the type of polymer associated with the bitumen, and the presence of cross-linking or stabilizing reagent, on the contrary, exert no influence on the phenomenon.